Many electronic devices include a user interface device for allowing user interaction and user input. One user interface device is a button or a key. Conventional buttons include mechanical components to actuate a switch to indicate a button press or button activation. Mechanical buttons also provide tactile feedback to the user to indicate the button has been pressed. More recently, touch-sensor buttons are being used in some applications to replace mechanical buttons.
One type of touch-sensor button operates by way of capacitance sensing, utilizing capacitance sensor electrodes. The capacitance detected by a capacitance sensor changes as a function of the proximity of a conductive object on or near the sensor electrode. The conductive object can be, for example, a stylus or a user's finger. In a touch-sensor button, a change in capacitance detected by each sensor due to the proximity of a conductive object can be measured by a variety of methods. Typically, an electrical signal representative of the capacitance detected by each capacitance sensor is processed by a processing device, which in turn produces electrical or optical signals representative of the button or sensor activation of the touch-sensor button.
However, mechanical buttons may still consume less power than capacitive sensor buttons because it is possible for mechanical buttons in the inactive state to not draw current, while still being responsive to input. In contrast, monitoring touch presence for existing capacitive sensor buttons may depend on the operation of various analog and digital circuits, thus increasing power demand even when the buttons are not being touched.